GHSA-4h3h-63v6-88qx
ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
esphomeReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
An integer overflow in the API component's protobuf decoder allows denial-of-service attacks when API encryption is not used.
Details
The bounds check ptr + field_length > end in components/api/proto.cpp can overflow when a malicious client sends a large field_length value. This affects all ESPHome device platforms (ESP32, ESP8266, RP2040, LibreTiny). The overflow bypasses the out-of-bounds check, causing the device to read invalid memory and crash.
When using the plaintext API protocol, this attack can be performed without authentication. When noise encryption is enabled, knowledge of the encryption key is required.
Affected Versions
ESPHome 2025.9.0 through 2025.12.6
Mitigation
- Upgrade to ESPHome 2025.12.7 or later (or 2026.1.0b3 or later)
- Enable API encryption with a unique key per device
- Follow the Security Best Practices
Severity
Low - Users following Security Best Practices with API encryption enabled are not affected without knowledge of the encryption key.
Impact
Denial-of-service. An attacker with network access to port 6053 can crash and reboot the device.
Credits
Thanks to @Mat931 for responsibly reporting this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | esphome | ≥ 2025.9.0&&< 2025.12.7 | 2025.12.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for esphome. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update esphome to 2025.12.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4h3h-63v6-88qx is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-4h3h-63v6-88qx is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-4h3h-63v6-88qx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-4h3h-63v6-88qx in your dependencies?
O3 detects GHSA-4h3h-63v6-88qx across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.